1. Field of the Invention
This invention relates generally to light detection and photodiode arrays, and in particular to arrays made from indium gallium arsenide and related materials.
2. Description of the Related Art
To extend the wavelength range of InxGa1-xAs detectors, the normal approach is to increase the Indium composition, or the x value [K. Linga, G. Olsen, V. Ban, A. Joshi, W. Kosonocky, “Dark current analysis and characterization of InxGa1-xAs/InAsyP1-y graded photodiodes with x>0.53 for response to longer wavelengths (>1.7 microns), Journal of Lightwave Technology, vol. 10, pp. 1050-2 (1992)], which is incorporated by reference herein.
FIG. 1 illustrates a description of this approach, where the substrate InP 1 has a buffer layer of InAsP 2 followed by the absorption layer InGaAs 3, followed by an InP cap 4. The InGaAs absorber 3 has a x-value that is greater than 0.53, and therefore is no longer lattice-matched with the InP substrate 1.
FIG. 2 illustrates the relationship of the x-value in InGaAs with the lattice-matching to InP substrate and the emission wavelength. By increasing the x-value from 0.53, the wavelength range is extended, but again, the material is no longer lattice-matched to the InP substrate 1. Because the material is no longer lattice-matched, dislocation defects are created in the material, which increase the dark current by several orders of magnitude over what the material should achieve theoretically. The InAsP buffer layer 2 is used to reduce the number of defects, but they cannot be completely eliminated because they propagate through the grown layer into the absorber. The InAsP buffer layer 2 also limits the short wavelength range which is normally limited by InP to a wavelength of 920 nm. The InAsP buffer layer 2 can increase the short wavelength to 1100 nm or higher, which is undesirable because it decreases the overall wavelength range to which the detector is responsive.
Other approaches have been made to extend the wavelength range in materials grown on InP substrates and GaAs substrates. One approach is to add Nitrogen to the InGaAs [D. Serries, T. Geppert, P. Ganser, M. Maier, K. Kohler, N. Herres, and J. Wagner, “Quaternary GaInAsN with high In content: Dependence of band gap energy on N content,” Applied Physics Letters, vol 80, no 14, pp. 2448-50], which is incorporated by reference herein. By growing thin layers of InGaAsN on InP, it has been demonstrated that the bandgap can be decreased to 590 meV, equivalent to a wavelength emission of 2.1 microns. However, the material exhibits poor photoluminescence which is indicative of a high concentration of defects.
Another approach introduces antimony (Sb) along with N to form InGaAsSbN to improve the photoluminescence [X. Yang, M. Jurkovic, J. Heroux, and W. Wang, “Molecular beam epitaxial growth InGaAsN:Sb/GaAs quantum wells for long-wavelength semiconductor lasers”, Applied Physics Letters, vol 75, no 2, pp. 178-80], which is incorporated by reference herein. The Sb is thought to act as a surfactant for the N and creates growth conditions that are more favorable for low defect growth, and devices made with such methods demonstrate laser emission wavelengths beyond 1 micron.
Thin layers of InGaAsSbN have been grown on InP to demonstrate extension of the laser emission wavelength [J. Fu, S. Bank, M. Wistey, H. Yuen, J. Harris, Jr., “Solid-source molecular-beam epitaxy growth of GaInNAsSb/InGaAs single quantum well on InP with photoluminescence peak wavelength at 2.04 microns,” Journal of Vacuum Science Technology B, vol. 22, no 3, pp. 1463-7], which is incorporated by reference herein. By using both N and Sb added to InGaAs, an extension of the wavelength from 1.7 microns to 2.04 microns was achieved, however, previous attempts to grow this material resulted in layers that were strained, and hence limited in thickness before dislocations occur. Therefore, they would not be useful for high-sensitivity, thick layer devices such as photodetectors.
It can be seen, then, that there is a need in the art for a material lattice-matched to InP that has an extended wavelength response. It can also be seen that there is a need in the art for growing thick-layer compositions on InP to produce devices. It can also be seen that there is a need in the art to reduce dislocation defects in such devices to decrease the dark current.